JP4940328B2 - Photoelectric conversion device - Google Patents

Description

  The present invention relates to a photoelectric conversion device, and particularly to a photoelectric conversion device including an intermediate layer.

  Solar cells using polycrystalline, microcrystalline, or amorphous silicon are known. In particular, a photoelectric conversion device having a structure in which thin films of microcrystalline silicon or amorphous silicon are stacked is attracting attention from the viewpoint of resource consumption, cost reduction, and efficiency.

  Generally, a photoelectric conversion device is formed by sequentially laminating a first electrode layer, one or more semiconductor thin film photoelectric conversion units, and a second electrode layer on a substrate having an insulating surface. Each photoelectric conversion unit is configured by stacking a p-type layer, an i-type layer, and an n-type layer from the light incident side. As a method for improving the conversion efficiency of the photoelectric conversion device, it is known to stack two or more photoelectric conversion units in the light incident direction. A first photoelectric conversion unit including a photoelectric conversion layer having a wide band gap is disposed on the light incident side of the photoelectric conversion device, and then a second photoelectric conversion layer including a photoelectric conversion layer having a narrower band gap than the first photoelectric conversion unit is disposed. A photoelectric conversion unit is arranged. Thereby, photoelectric conversion can be performed over a wide wavelength range of incident light, and the conversion efficiency of the entire apparatus can be improved.

  For example, as shown in FIG. 12, after forming the transparent electrode layer 12 on the substrate 10, the amorphous silicon photoelectric conversion unit (a-Si unit) 14 is used as the top cell, and the microcrystalline photoelectric conversion unit (μc-Si unit). A photoelectric conversion device 100 having a tandem structure with 16 as a bottom cell and having a back electrode layer 18 formed thereon is known.

  In such a tandem photoelectric conversion device 100, a configuration in which the intermediate layer 20 is provided between the a-Si unit 14 and the μc-Si unit 16 is known (see Patent Document 1). For example, zinc oxide (ZnO) or silicon oxide (SiOx) is used for the intermediate layer 20. The intermediate layer 20 may also be made of a silicon oxide material, a silicon carbide material, a silicon nitride material, a carbon material such as diamond-like carbon, or the like. The intermediate layer 20 has a light refractive index lower than that of the a-Si unit 14, and reflection of light to the a-Si unit 14 occurs between the a-Si unit 14 on the light incident side and the intermediate layer 20. ing.

JP 2004-260014 A

  However, when light is reflected by the intermediate layer 20 to the a-Si unit 14 on the light incident side, the a-Si unit 14, the transparent electrode layer 12, the substrate 10, air, and the refractive index become small, so the a-Si unit 14. The light reflected to the side escapes from the substrate 10, causing a problem that the light cannot be used sufficiently.

  One aspect of the present invention is a photoelectric conversion device in which a semiconductor film which is a p-type layer, an i-type layer, and an n-type layer is stacked, and is in contact with the i-type layer and within a refractive index range smaller than that of the i-type layer. The photoelectric conversion device includes an intermediate layer whose refractive index increases from a side in contact with the i-type layer toward a side not in contact with the i-type layer.

  ADVANTAGE OF THE INVENTION According to this invention, the utilization factor of the light in a photoelectric conversion apparatus can be improved and photoelectric conversion efficiency can be improved.

It is a cross-sectional schematic diagram which shows the structure of the photoelectric conversion apparatus in 1st Embodiment. It is a figure which shows the refractive index of the photoelectric conversion apparatus in 1st Embodiment. It is a figure which shows another example of the refractive index of the photoelectric conversion apparatus in 1st Embodiment. It is a cross-sectional schematic diagram which shows the structure of the photoelectric conversion apparatus in 2nd Embodiment. It is a cross-sectional schematic diagram which shows the structure of the photoelectric conversion apparatus in 3rd Embodiment. It is a figure which shows the refractive index of the photoelectric conversion apparatus in 3rd Embodiment. It is a figure which shows another example of the refractive index of the photoelectric conversion apparatus in 3rd Embodiment. It is a cross-sectional schematic diagram which shows the structure of the photoelectric conversion apparatus in 4th Embodiment. It is a cross-sectional schematic diagram which shows the structure of the photoelectric conversion apparatus in 5th Embodiment. It is a figure which shows the refractive index of the photoelectric conversion apparatus in 5th Embodiment. It is a figure which shows another example of the refractive index of the photoelectric conversion apparatus in 5th Embodiment. It is a cross-sectional schematic diagram which shows the structure of the conventional photoelectric conversion apparatus.

<First Embodiment>
FIG. 1 is a cross-sectional view illustrating a structure of a photoelectric conversion device 200 according to the first embodiment. The photoelectric conversion device 200 according to the present embodiment has an amorphous silicon photoelectric conversion unit (a-Si unit) having a wide band gap as a transparent conductive layer 32 and a top cell from the light incident side with the transparent insulating substrate 30 as the light incident side. 202 has a structure in which a microcrystalline silicon photoelectric conversion unit (μc-Si unit) 204 having a narrower band gap than the a-Si unit 202 and a back electrode layer 34 are stacked as a bottom cell.

For the transparent insulating substrate 30, for example, a material having transparency in at least a visible light wavelength region, such as a glass substrate or a plastic substrate, can be applied. A transparent conductive layer 32 is formed on the transparent insulating substrate 30. The transparent conductive layer 32 is doped with tin oxide (SnO ₂ ), zinc oxide (ZnO), indium tin oxide (ITO), etc. with tin (Sn), antimony (Sb), fluorine (F), aluminum (Al), etc. It is preferable to use at least one or a combination of a plurality of transparent conductive oxides (TCO). In particular, zinc oxide (ZnO) is preferable because it has high translucency, low resistivity, and excellent plasma resistance. The transparent conductive layer 32 can be formed by, for example, a sputtering method or a CVD method. The film thickness of the transparent conductive layer 32 is preferably in the range of 0.5 μm to 5 μm. Moreover, it is preferable to provide unevenness having a light confinement effect on the surface of the transparent conductive layer 32.

On the transparent conductive layer 32, the a-Si unit 202 is formed by sequentially laminating silicon-based thin films of the p-type layer 36, the i-type layer 38, and the n-type layer 40. The a-Si unit 202 includes a silicon-containing gas such as silane (SiH ₄ ), disilane (Si ₂ H ₆ ), dichlorosilane (SiH ₂ Cl ₂ ), a carbon hydrogen gas such as methane (CH ₄ ), diborane (B ₂ H). ₆ ) Plasma is formed from a mixed gas obtained by selecting a gas from a p-type dopant containing gas such as phosphine (PH ₃ ), a n-type dopant containing gas such as phosphine (PH ₃ ), and a diluting gas such as hydrogen (H ₂ ). It can be formed by a plasma CVD method. Specific film formation conditions are shown in Table 1.

  As the plasma CVD method, for example, an RF plasma CVD method of 13.56 MHz is preferably applied. The RF plasma CVD method can be a parallel plate type. In general, the p-type layer 36, the i-type layer 38, and the n-type layer 40 are formed in separate film formation chambers. The film formation chamber can be evacuated by a vacuum pump, and has an electrode for RF plasma CVD. Further, a transfer device for the transparent insulating substrate 30, a power source and matching device for the RF plasma CVD method, a pipe for supplying gas, and the like are attached.

  The p-type layer 36 is formed on the transparent conductive layer 32. The p-type layer 36 is a p-type amorphous silicon layer (p-type a-Si: H) or p-type amorphous silicon carbide layer (p-type a-SiC) having a thickness of 10 nm to 100 nm doped with a p-type dopant (boron or the like). : H) is preferred. The film quality of the p-type layer 36 can be changed by adjusting the mixing ratio of silicon-containing gas, hydrocarbon gas, p-type dopant-containing gas and dilution gas, pressure, and high-frequency power for plasma generation. The i-type layer 38 is an undoped amorphous layer formed on the p-type layer 36 and having a thickness of 50 nm to 500 nm. The film quality of the i-type layer 38 can be changed by adjusting the mixing ratio of the silicon-containing gas and the dilution gas, the pressure, and the high frequency power for plasma generation. The i-type layer 38 becomes a power generation layer of the a-Si unit 202. The n-type layer 40 is formed of an n-type amorphous silicon layer (n-type a-Si: H) having a thickness of 10 nm or more and 100 nm or less doped with an n-type dopant (such as phosphorus) formed on the i-type layer 38 or an n-type fine layer. A crystalline silicon layer (n-type μc-Si: H) is used. The film quality of the n-type layer 40 can be changed by adjusting the mixing ratio of the silicon-containing gas, the hydrocarbon gas, the n-type dopant-containing gas and the dilution gas, the pressure, and the high frequency power for plasma generation.

Next, the p-type layer 42, the first intermediate layer 44, the i-type layer 46, the second intermediate layer 48, and the n-type layer 50 are sequentially stacked to form the μc-Si unit 204. The μc-Si unit 204 includes a silicon-containing gas such as silane (SiH ₄ ), disilane (Si ₂ H ₆ ), dichlorosilane (SiH ₂ Cl ₂ ), a carbon hydrogen gas such as methane (CH ₄ ), diborane (B ₂ H ₆ ) Select a gas from a p-type dopant containing gas such as phosphine (PH ₃ ), an n-type dopant containing gas such as phosphine (PH ₃ ), an oxygen containing gas such as carbon dioxide (CO ₂ ), and a diluent gas such as hydrogen (H ₂ ). It can be formed by a plasma CVD method in which a mixed gas mixture is turned into plasma to form a film. Specific film forming conditions are shown in Table 2.

  As for the plasma CVD method, it is preferable to apply, for example, a 13.56 MHz RF plasma CVD method, similarly to the a-Si unit 202. In general, the p-type layer 42, the i-type layer 46, and the n-type layer 50 are formed in separate film formation chambers. Further, the first intermediate layer 44 and the second intermediate layer 48 may be formed using any one of the deposition chambers of the p-type layer 36, the n-type layer 40, the p-type layer 42, and the n-type layer 50. .

  The p-type layer 42 is formed on the n-type layer 40 of the a-Si unit 202. The p-type layer 42 is preferably a microcrystalline silicon layer, an amorphous silicon layer, or a combination thereof. The film quality of the p-type layer 42 can be changed by adjusting the mixing ratio of silicon-containing gas, hydrocarbon gas, p-type dopant-containing gas and dilution gas, pressure, and high-frequency power for plasma generation.

The first intermediate layer 44 is formed on the p-type layer 40. The first intermediate layer 44 plays a role of confining light in the i-type layer 46 that is the power generation layer of the μc-Si unit 204 together with the second intermediate layer 48 described later. The first intermediate layer 44 is preferably a layer containing silicon oxide doped with a p-type dopant (such as boron). For example, the first intermediate layer 44 is preferably formed by a plasma CVD method using a mixed gas in which an oxygen-containing gas such as carbon dioxide (CO ₂ ) is mixed into a silicon-containing gas, a p-type dopant-containing gas, and a diluent gas. It is. The film quality of the first intermediate layer 44 can be changed by adjusting the additive gas species, the gas mixture ratio, the pressure, and the high frequency power for plasma generation.

FIG. 2 shows the refractive index of each layer of the photoelectric conversion device 200 in this embodiment. As shown in FIG. 2, the refractive index n ₁ of the first intermediate layer 44 is made smaller than the refractive index n _i of the i-type layer 46 of the μc-Si unit 204 to be optically confined. The refractive index n ₁ of the first intermediate layer 44 is set to be equal to or lower than the refractive index n _p of the adjacent p-type layer 42. Furthermore, in the present embodiment, it is assumed that the refractive index of the first intermediate layer 44 is changed in the film thickness direction. As shown in FIG. 2, the first intermediate layer 44 is formed so that the refractive index n ₁ gradually increases from the i-type layer 46 side toward the p-type layer 42 side.

It is preferable that the refractive index n ₁ of the first intermediate layer 44 be substantially equal to the refractive index n _p of the p-type layer 42 at the interface with the p-type layer 42. Specifically, since the refractive index n _p of the p-type layer 42 is about 3.6, the refractive index n ₁ of the first intermediate layer 44 is about 3.6 at the interface with the p-type layer 42. It is preferable to do. The refractive index n ₁ of the first intermediate layer 44 is preferably as small as possible so that the film quality does not deteriorate at the interface with the i-type layer 46. Specifically, the refractive index n ₁ of the first intermediate layer 44 is preferably about 2.1 at the interface with the i-type layer 46.

In order to change the refractive index n ₁ of the first intermediate layer 44 in the film thickness direction, oxygen content such as carbon dioxide (CO ₂ ) with respect to a mixed gas of a silicon-containing gas, a dopant-containing gas, and a dilution gas is formed during film formation. What is necessary is just to change the mixing ratio of gas continuously. That is, in order to lower the refractive index n ₁ , the mixing ratio of oxygen-containing gas such as carbon dioxide (CO ₂ ) may be adjusted to be higher. Also, the refractive index n ₁ of the first intermediate layer 44 can be changed by adjusting the film forming conditions such as the pressure at the time of film formation of the first intermediate layer 44 by plasma CVD and the high frequency power for generating plasma.

  An i-type layer 46 is formed on the first intermediate layer 44. The i-type layer 46 is an undoped microcrystalline silicon film having a thickness of 0.5 μm to 5 μm. The i-type layer 46 is a layer that becomes a power generation layer of the μc-Si unit 204. The i-type layer 46 preferably has a laminated structure in which a buffer layer is first formed and a main power generation layer is formed on the buffer layer. The buffer layer is formed under a film formation condition that provides a higher crystallization rate than that of the main power generation layer. That is, when a single film is formed on a glass substrate or the like, the buffer layer is formed under film forming conditions that have a higher crystallization rate than the main power generation layer. The film quality of the i-type layer 46 can be changed by adjusting the mixing ratio of the silicon-containing gas and the dilution gas, the pressure, and the high frequency power for plasma generation.

The second intermediate layer 48 is formed on the i-type layer 46. The second intermediate layer 48 is preferably a layer containing silicon oxide doped with an n-type dopant (such as phosphorus). For example, the second intermediate layer 48 is preferably formed by a plasma CVD method using a mixed gas in which an oxygen-containing gas such as carbon dioxide (CO ₂ ) is mixed into a silicon-containing gas, an n-type dopant-containing gas, and a diluent gas. It is. The film quality of the second intermediate layer 48 can be changed by adjusting the additive gas species, the gas mixing ratio, the pressure, and the high frequency power for plasma generation.

As shown in FIG. 2, the refractive index n ₂ of the second intermediate layer 48 is made smaller than the refractive index n _i of the i-type layer 46 of the μc-Si unit 204 to be optically confined. The refractive index n ₂ of the second intermediate layer 48 is set to be _{equal to} or lower than the refractive index nn of the adjacent n-type layer 50. Furthermore, in the present embodiment, the second intermediate layer 48 is formed such that its refractive index n ₂ changes along the film thickness direction. As shown in FIG. 2, the second intermediate layer 48 is formed so that the refractive index n ₂ gradually increases from the i-type layer 46 side toward the n-type layer 50 side.

It is preferable that the refractive index n ₂ of the second intermediate layer 48 be substantially equal to the refractive index n _n of the n-type layer 50 at the interface with the n-type layer 50. Specifically, since the refractive index n _n of the n-type layer 50 is about 3.6, the refractive index n ₂ of the second intermediate layer 48 at the interface with the n-type layer 50 is about 3.6. It is preferable to do. The refractive index n ₂ of the second intermediate layer 48 is preferably as small as possible so that the film quality does not deteriorate at the interface with the i-type layer 46. Specifically, the refractive index n ₂ of the second intermediate layer 48 is preferably about 2.1 at the interface with the i-type layer 46.

In order to change the refractive index n ₂ of the second intermediate layer 48 in the film thickness direction, oxygen content such as carbon dioxide (CO ₂ ) with respect to a mixed gas of a silicon-containing gas, a dopant-containing gas, and a dilution gas is formed during film formation. What is necessary is just to change the mixing ratio of gas continuously. That may be adjusted to be higher the mixing ratio of the oxygen-containing gas such as carbon dioxide (CO ₂₎ and more reduce the refractive index n _2. Further, the refractive index n ₂ of the second intermediate layer 48 can be changed even by adjusting the film forming conditions such as the pressure at the time of film formation of the second intermediate layer 48 by plasma CVD and the high frequency power for plasma generation.

  The n-type layer 50 is formed on the second intermediate layer 48. The n-type layer 50 is an n-type microcrystalline silicon layer (n-type μc-Si: H) doped with an n-type dopant (such as phosphorus) and having a thickness of 5 nm to 50 nm. The film quality of the n-type layer 50 can be changed by adjusting the mixing ratio of silicon-containing gas, hydrocarbon gas, n-type dopant-containing gas and dilution gas, pressure, and high-frequency power for plasma generation.

  However, in this embodiment, the μc-Si unit 204 is not limited to this, and an i-type microcrystalline silicon layer (i-type μc-Si: H) is used for the i-type layer 46 serving as a power generation layer. What is necessary is just to provide the 1st intermediate | middle layer 44 and the 2nd intermediate | middle layer 48 so that the i-type layer 46 may be pinched | interposed.

A back electrode layer 34 is formed on the μc-Si unit 204. The back electrode layer 34 preferably has a laminated structure of a reflective metal and a transparent conductive oxide (TCO). As the transparent conductive oxide (TCO), tin oxide (SnO ₂ ), zinc oxide (ZnO), indium tin oxide (ITO), etc., or those doped with impurities are used. For example, zinc oxide (ZnO) doped with aluminum (Al) as an impurity may be used. Moreover, as a reflective metal, metals, such as silver (Ag) and aluminum (Al), are used. The transparent conductive oxide (TCO) and the reflective metal can be formed by, for example, a sputtering method or a CVD method. It is preferable that at least one of the transparent conductive oxide (TCO) and the reflective metal is provided with unevenness for enhancing the light confinement effect.

  Further, the back electrode layer 34 may be covered with a protective film (not shown). The protective film may be a resin material such as EVA or polyimide, and may be bonded so as to cover the back electrode layer 34 with a filler that is a similar resin material. This can prevent moisture from entering the power generation layer of the photoelectric conversion device 200.

  By using a YAG laser (fundamental wave 1064 nm, second harmonic 532 nm), the transparent conductive layer 32, the a-Si unit 202, the μc-Si unit 204, and the back electrode layer 34 are separated, so that a plurality of You may make it the structure which connected the cell in series.

  Hereinafter, the operation of the first intermediate layer 44 and the second intermediate layer 48 will be described. As indicated by an arrow (solid line) in FIG. 2, the light that has passed through the interface between the p-type layer 42 and the first intermediate layer 44 and entered the i-type layer 46 is transmitted to the i-type layer 46, the second intermediate layer 48, and the like. Are reflected by the difference in refractive index between them and returned to the i-type layer 46. Furthermore, when the light reflected at the interface between the i-type layer 46 and the second intermediate layer 48 reaches the interface between the i-type layer 46 and the first intermediate layer 44, it is reflected again by the difference in refractive index between the i-type layer 46 and the second intermediate layer 48. Return to 46. In this manner, the first intermediate layer 44 and the second intermediate layer 48 can provide an optical confinement effect on the i-type layer 46 of the μc-Si unit 204 serving as a bottom cell.

  In addition, as indicated by an arrow (broken line) in FIG. 2, a part of the light is transmitted through the interface between the i-type layer 46 and the second intermediate layer 48, but the light passes through the n-type layer 50 and n It reaches the mold layer 50 and the back electrode layer 34, is reflected by the refractive index difference between the n-type layer 50 and the back electrode layer 34, passes through the n-type layer 50 and the second intermediate layer 48, and returns to the i-type layer 46. Returned. Similarly to the above, the light reflected by the back electrode layer 34 is also confined in the i-type layer 46 by the first intermediate layer 44 and the second intermediate layer 48.

Here, by providing a gradient in the refractive index n ₁ , the refractive index difference (n _p −n ₁ ) at the interface between the p-type layer 42 and the first intermediate layer 44 is changed between the i-type layer 46 and the first intermediate layer 44. The refractive index difference (n _i −n ₁ ) of the interface is smaller and the light transmittance can be further improved with respect to light incident from the p-type layer 42 side. On the other hand, the light once incident on the i-type layer 46 is reflected at some place such as between the n-type layer 50 and the back electrode layer 34 and reaches the interface between the i-type layer 46 and the first intermediate layer 44. In this case, the reflectance to the i-type layer 46 can be increased by the refractive index difference (n _i −n ₁ ) at the interface between the i-type layer 46 and the first intermediate layer 44.

Further, by providing a gradient in the refractive index n ₂ , the refractive index difference (n _n −n ₂ ) at the interface between the n-type layer 50 and the second intermediate layer 48 is different between the i-type layer 46 and the second intermediate layer 48. The light transmittance can be improved with respect to light that is smaller than the refractive index difference (n _i −n ₂ ) at the interface and is reflected by the back electrode layer 34 or the like and incident from the n-type layer 50 side. . On the other hand, when the light once incident on the i-type layer 46 reaches the interface between the i-type layer 46 and the second intermediate layer 48, the refractive index difference (n _{i at} the interface between the i-type layer 46 and the second intermediate layer 48 _). -N ₂ ) can increase the reflectance to the i-type layer 46.

  In this way, it is possible to increase the light use efficiency in the i-type layer 46 of the μc-Si unit 204 serving as the bottom cell.

Here, the refractive index n ₁ of the first intermediate layer 44 at the interface with the p-type layer 42 is preferably larger than the refractive index n ₂ of the second intermediate layer 48 at the interface with the n-type layer 50. Since the refractive index n _n of the refractive index n _p and n-type layer 50 of p-type layer 42 is approximately the same size, the p-type layer 42 at the interface between the first intermediate layer 44, the n-type layer 50 The light introduction rate into the i-type layer 46 can be increased more than the interface with the second intermediate layer 48.

In addition, the film thickness d ₁ of the first intermediate layer 44 is preferably set to be equal to or less than the film thickness d ₂ of the second intermediate layer 48. Thereby, the reflectance at the interface between the first intermediate layer 44 and the i-type layer 46 is slightly lower than the reflectance at the interface between the i-type layer 46 and the second intermediate layer 48, but the light from the transparent insulating substrate 30 is reduced. Light absorption in the first intermediate layer 44 on the incident side is suppressed, the amount of light reaching the i-type layer 46 can be increased, and the power generation efficiency of the entire photoelectric conversion device 200 can be increased. On the other hand, the light absorption amount in the second intermediate layer 48 is larger than the light absorption amount in the first intermediate layer 44, but the light reflected from the back electrode layer 34 and incident on the second intermediate layer 48 is transparent. Light confinement to the i-type layer 46 is smaller than the light incident on the first intermediate layer 44 from the insulating substrate 30 side and increases the reflectance at the interface between the i-type layer 46 and the second intermediate layer 48. The effect is enhanced, and the power generation efficiency of the entire photoelectric conversion device 200 can be increased.

Specifically, the film thicknesses d ₁ and d ₂ of the first intermediate layer 44 and the second intermediate layer 48 are preferably 30 nm or more and 100 nm or less. In particular, the film thickness d ₁ of the first intermediate layer 44, a 50nm or less the range of 30 nm, the film thickness d ₂ of the second intermediate layer 48 is 50nm or more there is a thickness d ₁ or more first intermediate layer 44 A range of 100 nm or less is preferable.

Further, the refractive indexes n ₁ and n ₂ of the first intermediate layer 44 and the second intermediate layer 48 are not limited to being continuously inclined in the film thickness direction, but as shown in FIG. It may be changed to.

  The refractive index of each layer can be known by performing component analysis by energy dispersive X-ray analysis (EDX) on the cross section of the photoelectric conversion device 200. In the component analysis by EDX, when the content of oxygen (O) in the cross-sectional area of interest is higher than the other cross-sectional areas, it can be determined that the cross-sectional area of interest has a lower refractive index than the other cross-sectional areas. For example, the configuration of the photoelectric conversion device 200 according to the present embodiment is configured if layers having a higher oxygen content of oxygen (O) than the i-type layer 46 are provided on both sides of the i-type layer 46 of the μc-Si unit 204. It can be determined that it has. In addition, the refractive index relationship between the first intermediate layer 44 and the second intermediate layer 48 and the p-type layer 42 and the n-type layer 50 can be similarly determined.

  About the relationship of the refractive index of each layer, it can determine similarly also in other embodiment and modification which are mentioned later.

  In the present embodiment, layers containing silicon oxide doped with impurities are applied as the first intermediate layer 44 and the second intermediate layer 48. However, the present invention is not limited to this. For example, the first intermediate layer 44 and the second intermediate layer 48 may be a transparent conductive oxide (TCO) such as zinc oxide (ZnO). In particular, it is preferable to use zinc oxide (ZnO) doped with magnesium (Mg). The transparent conductive oxide (TCO) can be formed by, for example, a sputtering method or a CVD method.

<Second Embodiment>
As shown in FIG. 4, the photoelectric conversion device 206 in the second embodiment is provided with only the first intermediate layer 44 of the photoelectric conversion device 200 in the first embodiment and not the second intermediate layer 48. The configuration.

  In this case, the function of the first intermediate layer 44 is the same as that of the photoelectric conversion device 200 in the first embodiment. On the other hand, since the second intermediate layer 48 is not provided, the light transmitted through the interface between the p-type layer 42 and the first intermediate layer 44 and incident on the i-type layer 46 is the n-type layer 50 and the back electrode layer 34. And is returned to the i-type layer 46. When the reflected light reaches the interface between the i-type layer 46 and the first intermediate layer 44, it is reflected again by the difference in refractive index between the i-type layer 46 and the i-type layer 46. In this manner, the first intermediate layer 44 and the back electrode layer 34 provide a light confinement effect on the i-type layer 46 of the μc-Si unit 204 serving as the bottom cell.

  Note that only the second intermediate layer 48 may be provided without providing the first intermediate layer 44. In this case, the function of the second intermediate layer 48 is the same as that of the photoelectric conversion device 200 in the first embodiment. Since the first intermediate layer 44 is not provided, the light confinement effect on the i-type layer 46 is reduced, but the reflection effect by the second intermediate layer 48 is obtained.

<Third Embodiment>
FIG. 5 is a cross-sectional view illustrating the structure of the photoelectric conversion device 300 according to the third embodiment. The photoelectric conversion device 300 according to the present embodiment is different from the photoelectric conversion device 200 according to the first embodiment in that, instead of providing the first intermediate layer 44 and the second intermediate layer 48 in the μc-Si unit 204, the a-Si The unit 202 is provided with a first intermediate layer 52 and a second intermediate layer 54. The method for forming each layer is the same as that in the first embodiment, and thus the description thereof is omitted.

FIG. 6 shows the refractive index of each layer of the photoelectric conversion device 300 in this embodiment. As shown in FIG. 6, the refractive index n ₂ of the refractive index n ₁ and a second intermediate layer 54 of the first intermediate layer 52, the refractive index of the i-type layer 38 of a-Si unit 202 as a target of optical confinement n _Make it smaller than _ai . Further, the refractive index n ₁ of the first intermediate layer 52 is set to be equal to or lower than the refractive index n _ap of the adjacent p-type layer 36. The refractive index n ₂ of the second intermediate layer 54 is set to be equal to or lower than the refractive index n _an of the adjacent n-type layer 40.

Furthermore, in the present embodiment, it is assumed that the refractive index of the first intermediate layer 52 is changed in the film thickness direction. As shown in FIG. 6, the first intermediate layer 52 is formed so that the refractive index n ₁ gradually increases from the i-type layer 38 side to the p-type layer 36 side. Furthermore, the second intermediate layer 54 is formed such that its refractive index n ₂ changes along the film thickness direction. As shown in FIG. 6, the second intermediate layer 54 is formed so that the refractive index n ₂ gradually increases from the i-type layer 38 side to the n-type layer 40 side.

The refractive index n ₁ of the first intermediate layer 52 is preferably substantially equal to the refractive index n _ap of the p-type layer 36 at the interface with the p-type layer 36. Specifically, since the refractive index n _ap of the p-type layer 36 is about 3.6, the refractive index n ₁ of the first intermediate layer 52 at the interface with the p-type layer 36 is about 3.6. It is preferable to do. The refractive index n ₁ of the first intermediate layer 52 is preferably as small as possible so that the film quality does not deteriorate at the interface with the i-type layer 38. Specifically, the refractive index n ₁ of the first intermediate layer 52 is preferably about 2.1 at the interface with the i-type layer 38.

The refractive index n ₂ of the second intermediate layer 54 is preferably made substantially equal to the refractive index n _an of the n-type layer 40 at the interface with the n-type layer 40. Specifically, since the refractive index n _an of the n-type layer 40 is about 3.6, the refractive index n ₂ of the second intermediate layer 54 at the interface with the n-type layer 40 is about 3.6. It is preferable to do. The refractive index n ₂ of the second intermediate layer 54 is preferably as small as possible so that the film quality does not deteriorate at the interface with the i-type layer 38. Specifically, the refractive index n ₂ of the second intermediate layer 54 is preferably about 2.1 at the interface with the i-type layer 38.

  Hereinafter, the operation of the first intermediate layer 52 and the second intermediate layer 54 will be described. As indicated by an arrow (solid line) in FIG. 6, the light that has passed through the interface between the p-type layer 36 and the first intermediate layer 52 and entered the i-type layer 38 is transmitted to the i-type layer 38, the second intermediate layer 54, and the like. Are reflected by the difference in refractive index between them and returned to the i-type layer 38. Further, when the light reflected at the interface between the i-type layer 38 and the second intermediate layer 54 reaches the interface between the i-type layer 38 and the first intermediate layer 52, it is reflected again by the difference in refractive index between the i-type layer 38 and the second intermediate layer 54. Return to 38. In this manner, the first intermediate layer 52 and the second intermediate layer 54 can provide a light confinement effect on the i-type layer 38 of the a-Si unit 202 serving as the top cell.

  In addition, as indicated by an arrow (broken line) in FIG. 6, a part of light is transmitted through the interface between the i-type layer 38 and the second intermediate layer 54, but the light is transmitted through the n-type layer 40 and the p-type layer 42. The n-type layer 46 and the n-type layer 50 are passed through to reach the n-type layer 50 and the back electrode layer 34, and are reflected by the difference in refractive index between the n-type layer 50 and the back electrode layer 34, and then the i-type layer again. Return to 38. Similarly to the above, the light reflected by the back electrode layer 34 is confined in the i-type layer 38 by the first intermediate layer 52 and the second intermediate layer 54.

Here, by providing a gradient in the refractive index n ₁ , the refractive index difference (n _ap −n ₁ ) at the interface between the p-type layer 36 and the first intermediate layer 52 is changed between the i-type layer 38 and the first intermediate layer 52. The refractive index difference (n _ai −n ₁ ) at the interface is smaller and the light transmittance can be further improved with respect to light incident from the p-type layer 36 side. On the other hand, when the light once incident on the i-type layer 38 is reflected at the interface between the second intermediate layer 54 and the n-type layer 40 and reaches the interface between the i-type layer 38 and the first intermediate layer 52, The reflectance to the i-type layer 38 can be increased by the refractive index difference (n _ai −n ₁ ) at the interface between the layer 38 and the first intermediate layer 52.

Further, by providing a gradient in the refractive index n ₂ , the difference in refractive index (n _an −n ₂ ) at the interface between the n-type layer 40 and the second intermediate layer 54 is different between the i-type layer 38 and the second intermediate layer 54. The light transmittance can be improved for light that is smaller than the refractive index difference (n _ai −n ₂ ) at the interface and is reflected by the back electrode layer 34 or the like and incident from the n-type layer 40 side. . On the other hand, when the light once incident on the i-type layer 38 reaches the interface between the i-type layer 38 and the second intermediate layer 54, the refractive index difference ( _{nai) at} the interface between the i-type layer 38 and the second intermediate layer 54. -N ₂ ) can increase the reflectance to the i-type layer 46.

  In this way, it is possible to increase the light use efficiency in the i-type layer 38 of the a-Si unit 202 that becomes the top cell.

Here, the refractive index n ₁ of the first intermediate layer 52 at the interface with the p-type layer 36 is preferably larger than the refractive index n ₂ of the second intermediate layer 54 at the interface with the n-type layer 40. Since the refractive index n _an, the refractive index n _ap and n-type layer 40 of p-type layer 36 is approximately the same size, the p-type layer 36 at the interface between the first intermediate layer 52, the n-type layer 40 The light introduction rate into the i-type layer 38 can be increased more than the interface with the second intermediate layer 54.

In addition, the film thickness d ₁ of the first intermediate layer 52 is preferably set to be equal to or less than the film thickness d ₂ of the second intermediate layer 54. Thereby, the reflectance at the interface between the first intermediate layer 52 and the i-type layer 38 is somewhat lower than the reflectance at the interface between the i-type layer 38 and the second intermediate layer 54, but the light from the transparent insulating substrate 30 Light absorption in the first intermediate layer 52 on the incident side is suppressed, the amount of light reaching the i-type layer 38 can be increased, and the power generation efficiency of the entire photoelectric conversion device 300 can be increased. On the other hand, the light absorption amount in the second intermediate layer 54 is larger than the light absorption amount in the first intermediate layer 52, but the light reflected and incident on the second intermediate layer 54 is from the transparent insulating substrate 30 side. By increasing the reflectance at the interface between the i-type layer 38 and the second intermediate layer 54 that is smaller than the light incident on the first intermediate layer 52, the light confinement effect on the i-type layer 38 is increased, and the photoelectric The power generation efficiency of the conversion device 300 as a whole can be increased.

Specifically, the film thicknesses d ₁ and d ₂ of the first intermediate layer 52 and the second intermediate layer 54 are preferably 30 nm or more and 100 nm or less. In particular, the film thickness d ₁ of the first intermediate layer 52 is in the range of 30 nm or more and 50 nm or less, and the film thickness d ₂ of the second intermediate layer 54 is greater than or equal to the film thickness d ₁ of the first intermediate layer 52 and is 50 nm or more. A range of 100 nm or less is preferable.

Further, the refractive indexes n ₁ and n ₂ of the first intermediate layer 52 and the second intermediate layer 54 are not limited to being continuously inclined in the film thickness direction, but are stepped as shown in FIG. It may be changed to.

  In this embodiment, the first intermediate layer 52 and the second intermediate layer 54 include layers containing silicon oxide doped with impurities. However, the present invention is not limited to this. For example, the first intermediate layer 52 and the second intermediate layer 54 may be a transparent conductive oxide (TCO) such as zinc oxide (ZnO). In particular, it is preferable to use zinc oxide (ZnO) doped with magnesium (Mg). The transparent conductive oxide (TCO) can be formed by, for example, a sputtering method or a CVD method.

<Fourth embodiment>
As shown in FIG. 8, the photoelectric conversion device 302 according to the fourth embodiment is provided with only the second intermediate layer 54 of the photoelectric conversion device 300 according to the third embodiment, and is not provided with the first intermediate layer 52. The configuration.

  In this case, the function of the second intermediate layer 54 is the same as that of the photoelectric conversion device 300 in the third embodiment. By providing the second intermediate layer 54, the reflection of light to the i-type layer 38 can be enhanced, and the power generation efficiency in the a-Si unit 202 serving as the top cell can be enhanced.

  Note that only the first intermediate layer 52 may be provided without providing the second intermediate layer 54. In this case, the function of the first intermediate layer 52 is the same as that of the photoelectric conversion device 300 in the third embodiment. On the other hand, since the second intermediate layer 54 is not provided, the light that has not been absorbed by the i-type layer 38 reaches the back electrode layer 34 through the n-type layer 40 and the μc-Si unit 204 serving as a bottom cell. When it is reflected and is not absorbed by the μc-Si unit 204 that becomes the bottom cell, it is returned to the i-type layer 38. When the reflected light reaches the interface between the i-type layer 38 and the first intermediate layer 52, the reflected light is reflected again by the difference in refractive index between them and returned to the i-type layer 38. In this way, the first intermediate layer 52 and the back electrode layer 34 provide an optical confinement effect on the a-Si unit 202 serving as the top cell and the μc-Si unit 204 serving as the bottom cell.

  Furthermore, it is good also as a structure which combined the structure in 1st-4th embodiment suitably. Thereby, effects, such as optical confinement in each, can be synergistically obtained, and the power generation efficiency of the photoelectric conversion device can be further increased.

<Fifth embodiment>
The present invention can be applied to a crystalline photoelectric conversion device. FIG. 9 is a schematic cross-sectional view illustrating the structure of a photoelectric conversion device 400 including the single crystal silicon layer 60.

  The photoelectric conversion device 400 sequentially forms the first intermediate layer 62, the intrinsic semiconductor layer 64, and the conductive semiconductor layer 66 on the surface (first surface) of the single crystal silicon layer 60, and the back surface (second surface) of the single crystal silicon layer 60. The second intermediate layer 68, the intrinsic semiconductor layer 70, and the conductive semiconductor layer 72 are formed on the surface).

  The single crystal silicon layer 60 is preferably n-type single crystal silicon (resistivity = about 0.5 to 4 Ωcm). For example, the single crystal silicon layer 60 is preferably a 100 mm square and has a thickness of about 100 to 500 μm.

  A first intermediate layer 62 is formed on the surface (first surface) of the single crystal silicon layer 60. The first intermediate layer 62 can be formed in the same manner as the first intermediate layer 44 in the first embodiment. On the first intermediate layer 62, there are an intrinsic semiconductor layer 64 (film thickness: about 50 to 200 mm) which is an amorphous silicon layer which is not doped by plasma CVD, and a p-type amorphous silicon layer to which a p-type dopant is added. A certain conductive semiconductor layer 66 (film thickness: about 50 to 150 mm) is formed. Note that although the intrinsic semiconductor layer 64 and the conductive semiconductor layer 66 are amorphous silicon, microcrystalline silicon may be used.

  A second intermediate layer 68 is formed on the back surface (second surface) of the single crystal silicon layer 60. The second intermediate layer 68 can be formed in the same manner as the second intermediate layer 48 in the first embodiment. On the second intermediate layer 68, there are an intrinsic semiconductor layer 70 (film thickness: about 50 to 200 あ る) which is an amorphous silicon layer which is not doped using a plasma CVD method, and an n-type amorphous silicon layer to which an n-type dopant is added. A certain conductive semiconductor layer 72 (film thickness: about 100 to 500 mm) is formed. Note that although the intrinsic semiconductor layer 70 and the conductive semiconductor layer 72 are amorphous silicon, microcrystalline silicon may be used.

  On the conductive semiconductor layers 66 and 72, transparent conductive layers 74 and 76 having substantially the same area as these are formed. Further, collector electrodes 78 and 80 made of silver paste or the like are formed on the transparent conductive layers 74 and 76. In the photoelectric conversion device 400, since the transparent conductive layer 76 is also used on the back surface (second surface) side, even if light enters the back surface side, it contributes to power generation.

FIG. 10 shows the refractive index of each layer of the photoelectric conversion device 400. As shown in FIG. 10, the refractive index n ₂ of the refractive index n ₁ and the second intermediate layer 68 of the first intermediate layer 62 is smaller than the refractive index n _ci of the target optical confinement single crystal silicon layer 60 . The refractive index n ₁ of the first intermediate layer 62 is set to be equal to or lower than the refractive index n _pi of the adjacent intrinsic semiconductor layer 64 and conductive semiconductor layer 66. Furthermore, in the present embodiment, the refractive index n ₁ of the first intermediate layer 62 is changed in the film thickness direction. As shown in FIG. 10, the first intermediate layer 62 is formed so that the refractive index n ₁ gradually increases from the single crystal silicon layer 60 side toward the intrinsic semiconductor layer 64 side.

The refractive index n ₂ of the second intermediate layer 68 is set to be equal to or lower than the refractive index n _ni of the adjacent intrinsic semiconductor layer 70 and conductive semiconductor layer 72. Furthermore, in the present embodiment, it is assumed that the refractive index n ₂ of the second intermediate layer 68 is changed in the film thickness direction. The second intermediate layer 68 is formed so that the refractive index n ₂ gradually increases from the single crystal silicon layer 60 side toward the intrinsic semiconductor layer 70 side.

  As a result, as indicated by an arrow (solid line) in FIG. 10, the light incident on the single crystal silicon layer 60 through the interface between the intrinsic semiconductor layer 64 and the first intermediate layer 62 is transmitted to the single crystal silicon layer 60 and the first crystal layer 60. Reflected by the difference in refractive index between the two intermediate layers 68 and returned to the single crystal silicon layer 60. Furthermore, when the light reflected at the interface between the single crystal silicon layer 60 and the second intermediate layer 68 reaches the interface between the single crystal silicon layer 60 and the first intermediate layer 62, it is reflected again due to the difference in refractive index between them. Returned to the crystalline silicon layer 60. Further, as indicated by an arrow (broken line) in FIG. 10, the light that has entered the single crystal silicon layer 60 through the interface between the intrinsic semiconductor layer 70 and the second intermediate layer 68 is transmitted to the single crystal silicon layer 60 and the first crystal layer 60. Reflected by the difference in refractive index between each other at the interface with the intermediate layer 62 and returned to the single crystal silicon layer 60. Further, when reaching the interface between the single crystal silicon layer 60 and the second intermediate layer 68, it is reflected again by the difference in refractive index and returned to the single crystal silicon layer 60. In this manner, the first intermediate layer 62 and the second intermediate layer 68 can provide an optical confinement effect on the single crystal silicon layer 60.

Here, by providing a gradient in the refractive index n ₁ , the refractive index difference (n _pi −n ₁ ) at the interface between the intrinsic semiconductor layer 64 and the first intermediate layer 62 is changed to the single crystal silicon layer 60 and the first intermediate layer 62. The refractive index difference (n _ci −n ₁ ) at the interface between the _first semiconductor layer 64 and the light incident from the intrinsic semiconductor layer 64 side can be improved. On the other hand, the light once incident on the single crystal silicon layer 60 is reflected at some place such as between the intrinsic semiconductor layer 70 and the back electrode layer 76 and is reflected at the interface between the single crystal silicon layer 60 and the first intermediate layer 62. When it reaches, the reflectance to the single crystal silicon layer 60 can be increased by the refractive index difference (n _ci −n ₁ ) at the interface between the single crystal silicon layer 60 and the first intermediate layer 62.

Further, by providing a gradient in the refractive index n ₂ , the refractive index difference (n _ni −n ₂ ) at the interface between the intrinsic semiconductor layer 70 and the second intermediate layer 68 can be reduced between the single crystal silicon layer 60 and the second intermediate layer 68. The refractive index difference (n _ci −n ₂ ) of the interface is smaller, and the light transmittance can be improved for light incident from the intrinsic semiconductor layer 70 side. On the other hand, when the light once incident on the single crystal silicon layer 60 reaches the interface between the single crystal silicon layer 60 and the second intermediate layer 68, the refractive index difference at the interface between the single crystal silicon layer 60 and the second intermediate layer 68. By (n _ci −n ₂ ), the reflectance to the single crystal silicon layer 60 can be increased.

  As described above, by providing the first intermediate layer 62 and the second intermediate layer 68, the light confinement effect in the single crystal silicon layer 60 can be obtained, and the light use efficiency can be improved.

It is preferable that the refractive index n ₁ of the first intermediate layer 62 be substantially equal to the refractive index n _pi of the intrinsic semiconductor layer 64 at the interface with the intrinsic semiconductor layer 64. The refractive index n ₂ of the second intermediate layer 68 is preferably substantially equal to the refractive index n _ni of the intrinsic semiconductor layer 70 at the interface with the intrinsic semiconductor layer 70. The refractive index n ₂ of the refractive index n ₁ and the second intermediate layer 68 of the first intermediate layer 62, the film quality at the interface between the single crystal silicon layer 60 is preferable to be as small as possible so as not to decrease.

In addition, the film thickness d ₁ of the first intermediate layer 62 is preferably set to be equal to or less than the film thickness d ₂ of the second intermediate layer 68. As a result, the reflectance at the interface between the first intermediate layer 62 and the single crystal silicon layer 60 is somewhat lower than the reflectance at the interface between the single crystal silicon layer 60 and the second intermediate layer 68, but the main light is incident. Light absorption in the first intermediate layer 62 disposed on the side is suppressed, the amount of light reaching the single crystal silicon layer 60 can be increased, and the power generation efficiency of the entire photoelectric conversion device 400 can be increased. On the other hand, the light absorption amount in the second intermediate layer 68 is larger than the light absorption amount in the first intermediate layer 62, but the light that passes through the second intermediate layer 68 and reaches the single crystal silicon layer 60 is the first amount. It is smaller than the light that passes through the intermediate layer 62 and reaches the single crystal silicon layer 60, and increases the reflectivity at the interface between the single crystal silicon layer 60 and the second intermediate layer 68, thereby improving the single crystal silicon layer 60. The light confinement effect is enhanced, and the power generation efficiency of the entire photoelectric conversion device 400 can be increased.

Further, the refractive indexes n ₁ and n ₂ of the first intermediate layer 62 and the second intermediate layer 68 are not limited to being continuously inclined in the film thickness direction, but as shown in FIG. It may be changed to.

  By providing at least one of the first intermediate layer 62 and the second intermediate layer 68, an effect of improving the power generation efficiency of the photoelectric conversion device can be obtained. Further, even in a photoelectric conversion device in which two or more single crystal silicon layers 60 as power generation layers are stacked, a light confinement effect can be obtained by providing the first intermediate layer 62 or the second intermediate layer 68 for each single crystal silicon layer 60. Can do.

  10 substrate, 12 transparent conductive layer, 14 amorphous silicon photoelectric conversion unit (a-Si unit), 16 microcrystalline silicon photoelectric conversion unit (μc-Si unit), 20 intermediate layer, 30 transparent insulating substrate, 32 transparent conductive layer, 34 Back electrode layer, 36 p-type layer (a-Si), 38 i-type layer (a-Si), 40 n-type layer (a-Si), 42 p-type layer (μc-Si), 44, 56, 62 1 intermediate layer, 46 i-type layer (μc-Si), 48, 58, 68 2nd intermediate layer, 50 n-type layer (μc-Si), 60 single crystal silicon layer, 64 intrinsic semiconductor layer, 66 conductive semiconductor layer , 70 Intrinsic semiconductor layer, 72 Conductive semiconductor layer, 74, 76 Transparent conductive layer, 78, 80 Collector electrode, 100, 200, 206, 300, 302, 400 Photoelectric conversion device, 202 Amorphous silicon Photoelectric conversion unit (a-Si unit), 204 microcrystalline silicon photoelectric conversion unit (μc-Si unit).

Claims (3)

A photoelectric conversion device in which semiconductor films that are p-type layers, i-type layers, and n-type layers are stacked,
An intermediate layer in contact with the i-type layer and having a refractive index that increases from a side in contact with the i-type layer within a range of refractive index smaller than the i-type layer toward a side not in contact with the i-type layer ;
The said intermediate | middle layer is provided with the 1st intermediate | middle layer and 2nd intermediate | middle layer which are arrange | positioned so that the said i-type layer may be pinched | interposed, The photoelectric conversion apparatus characterized by the above-mentioned. The photoelectric conversion device according to claim 1 ,
The first intermediate layer is disposed closer to the light incident surface than the second intermediate layer,
The photoelectric conversion device according to claim 1, wherein a refractive index on a side of the first intermediate layer in contact with the i-type layer is larger than a refractive index on a side of the second intermediate layer in contact with the i-type layer. The photoelectric conversion device according to claim 1 , wherein
The photoelectric conversion device, wherein the first intermediate layer is disposed closer to the light incident surface than the second intermediate layer, and has a thickness equal to or smaller than the second intermediate layer.

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